The refractive index of a probe volume is in general a complex number comprising a real part and an imaginary part which both depend on the space coordinates. The complex spatial distribution of the refractive index of a probe volume is referred to here as the “optical properties” of that probe volume.
There is a need for interrogating the optical properties of an array of probe volumes in a variety of applications including Biomedical Diagnostics, Genomics, Proteomics, Drug Discovery, DNA Sequencing, Optical Data Storage, Material Science, Occupational Health and Safety, Civilian or Military Counterterrorism, Battlefield, Electrophoresis, Analytical Chromatography, Semiconductor Processing, Metrology, Counterfeiting, Food Processing, Forensics, Law Enforcement, Environmental Monitoring, Microscopy, Mass Spectroscopy, Microfluidic Dynamics, and Flow Cytometry. In many of these applications the optical properties of a probe volume that includes a sample of a material of interest (target specimen probe volume) are compared with the optical properties of a probe volume including a sample of a material of reference (reference sample probe volume). Thus a convenient approach is to determine the comparative optical properties of the target specimen probe volume relative to one or more reference sample probe volume(s). For example, a group of molecules of a first type (first target specimen) occupy a portion of a target specimen probe volume. A solution of a group of molecules of a second type (second target specimen) in a liquid (third target specimen) is delivered to the target specimen probe volume and then washed off. The apparatus reveals if a reaction between the first and second type of molecules has occurred by interrogating the optical properties of the target specimen probe volume which may have changed if the second type of molecules have occupied part of it by binding to the first type of molecules. Known apparatuses and methods for performing this comparison often involve the use of multiple measurements, multiple separate probe beams, complex apparatuses for scanning or changing probe beam positions, or other relatively complex approaches to realize the multiple comparative measurements.